2.1 SALTS OF AMINOIMIDAZOLE CARBOXAMIDE
AICA is referred to as "Orazamide" in the literature. Orazamide, a salt of aminoimidazole carboxamide (hereinafter referred "AICA"), has been used as a hepatoprotectant based on its ability to prevent necrosis and stimulate regeneration of the liver parenchymal cells.
2.1.1 CHEMICAL NATURE AND PROPERTIES OF SALTS OF AMINOIMIDAZOLE CARBOXAMIDE
Orazamide is available in different forms as: 5-aminoimidazole-4-carboxamide orotate, 4-amino-5-imidazole carboxamide orotate or a combination of 1,2,3,6-tetrahydro-2,6-dioxo-4-pyrimidine carboxylic acid with 5-amino-1H-imidazole-4-carboxamide (1:1) or a combination of orotic acid with 5(or 4)-aminoimidazole-4(or 5)-carboxamide (1:1). The C.sub.5 amine group on the imidazole ring can be attached to the C.sub.4 carboxyl group of orotic acid or any other organic acid which is chemically compatible with the body.
The known pharmacological activity of AICA orotate or orazamide resides in AICA and/or orotic acid. AICA is incorporated into animal nucleic acids, especially in purine biosynthesis. Orotic acid, also found in milk, is a pyrimidine precursor in animal organisms. Thus, AICA orotate contains precursors of purine and pyrimidine components of nucleic acids and its application as a hepatoprotectant was based on its stimulatory effects on regeneration of liver parenchymal cells. ##STR1##
2.1.2 PHARMACOKINETICS OF AICA SALTS
Orazamide or AICA orotate is currently used as a hepatoprotectant. AICA has been found to prevent liver necrosis and stimulate regeneration of the liver parenchymal cells. Upon administration of an AICA salt, AICA is the major metabolite.
2.1.3 AICA SALTS AND CANCER
The observation that AICA is utilized as a precursor in purine biosynthesis by normal and tumor cells suggested that an analog of AICA may exert an antitumor activity by inhibiting the biosynthetic pathway to nucleic acids. Hano, K., and Akashi, A., 1964, Gann 55:25-35. Therefore, a series of triazenoimidazoles, analogs of AICA in which the 5-amino group has been replaced by various monoalkyl- and dialkyltriazeno groups, has been synthesized and evaluated for antitumor activity. Shealy, Y. F., and Kranth, C. A., 1966, J. Med. Chem. 9:34-38, Shealy, Y. F., et al., 1962, J. Org. Chem. 27:2150-2154; and Shealy, Y. F., et al., 1961, J. Org. Chem. 26:2396-2401. One of these analogs, 5-(dimethyltriazeno) imidazole-4-carboxamine (DTIC or DTIC-Dome, Dacarbazine), having the following formula: ##STR2## has exhibited notable activity against mouse sarcoma 180, adenocarcinoma 755, leukemia L1210 (Shealy, Y. F., et al., 1962, Biochem. Pharmacol. 11:674-676) and melanoma cells, (Rutty, C. J., et al., 1984, Br. J. Cancer 48:140).
Dacarbazine or DTIC-Dome is used as an anticancer agent in humans. After intravenous administration of DTIC-Dome, the volume of distribution exceeds total body water content suggesting localization in some body tissue, probably the liver. Its disappearance from the plasma is biphasic with an initial half-life of 19 minutes and a terminal half-life of 5 hours. The average cumulative excretion of unchanged DTIC in the urine is 40% of the injected dose in 6 hours. DTIC is subject to renal tubular secretion rather than glomerular filtration. At therapeutic concentrations DTIC is not appreciably bound to human plasma protein. DTIC is degraded extensively in man. Besides unchanged DTIC, 5-aminoimidazole-4-carboxamide (AICA) is the major metabolite of DTIC excreted in the urine. AICA is not derived endogenously, but from the injected DTIC, because the administration of radioactive DTIC labeled with .sup.14 C in the imidazole portion of the molecule (DTIC-2-.sup.14 C) gives rise to AICA-2-.sup.14 C. Although the exact mechanism of action of DTIC-Dome is not known, three hypotheses have been offered: 1) inhibition of DNA synthesis by acting as a purine analog; 2) action as an alkylating agent; and 3) interaction with SH groups. DTIC-Dome is indicated in the treatment of metastatic malignant melanoma. In addition, DTIC-Dome is also indicated for Hodgkin's disease as a secondary-line therapy when used in combination with other effective agents.
Even though AICA is the major metabolite of DTIC, there is no suggestion in the prior art nor any evidence to indicate whether the AICA formed is important in bringing about the anti-tumor and/or antimetastatic effect of DTIC-Dome. There is no prior art to suggest that DTIC-Dome may be a prodrug for AICA. The term "prodrug" as used herein describes pharmacologically inactive chemical derivatives of a drug molecule that require a transformation within the body in order to release the active drug. In fact, analogs of AICA such as DTIC-Dome were developed with the objective of blocking and/or competing with AICA and interfering with the synthesis of nucleic acids. In this regard, there is one report by Hakala et al., 1964, Biochem. Biophys. Acts. 80:666-668, indicating that AICA prevented the growth inhibitory effects of the chemotherapeutic agent, 6-mercaptopurine on tumor cells in vitro. However, in this connection, it has also been reported that AICA has been found to be able to prevent 6-mercaptopurine induced suppression of lymphocyte responsiveness in vitro. Al-Safi, S. A., and Maddocks, J. L., 1984, Br. J. Clin. Pharmac. 17:417-422. In addition, AICA was found to exhibit an antioxidant activity and increase the superoxide dismutase expression in lymphocytes incubated in vitro. Muzes, G., et al., 1990, Acta Physiologica Hungarica 76:183-190. The use of AICA alone or in combination with a cancer chemotherapeutic agent has not been reported for the prevention and treatment of primary and metastatic neoplastic diseases and other diseases.
2.2 SALTS OF 5-AMINO OR SUBSTITUTED AMINO 1,2,3-TRIAZOLES
5-amino or substituted amino 1,2,3-triazoles were originally disclosed as having anticoccidial activity in poultry (U.S. Pat. No. 4,590,201, issued May 20, 1986), and later as cancer treatment agents in the treatment of peritoneal carcinomatosis of ovarian cancer (U.S. Pat. No. 5,132,315, issued Jul. 21, 1992 and Kohn E. C. et al., 1990, J. Natl Cancer Inst. 82:54-60) and as antimetastatic agents in the PMT-6 fibrosarcoma tumor model in mice (U.S. Pat. No. 5,045,543, issued Sep. 3, 1991). One 1,2,3-triazole-4-carboxamide compound in particular, 5-amino-1-(4-4-chlorobenzoyl!-3,5-dichlorobenzyl-1,2,3-triazole-4-carboxa mide, designated L651582 (Merck Research Laboratories, U.S. Pat. No. 4,590,201) and having the following formula: ##STR3## was also shown to inhibit cell proliferation, inflammation and some signal transduction pathways including those which involve calcium influx, the release of arachidonic acid and the generation of inositol phosphates. Kohn, E. C. et al., 1992, Cancer Res. 52:3208-3212 and Felder, et al., 1991, J. Pharmacolol. Exp. Ther. 257:967-971.
Arachidonic acid and/or its eicosanoid metabolites have been implicated in different stages of malignancies and a large variety of diseases including, but not limited to, psoriasis, eczema, systemic lupus erythematosus or arthritis. Pharmacologic inhibition of eicosanoid synthesis in animal models and humans has resulted in inhibition of development and progression of cancer and other diseases. Karmali, R. A., et al., 1982, Prostaglandins and Med 8:437-446; and Karmali, R. A., et al., 1985, Prostaglandins Leuk Med 20:283-286. L651582 has been demonstrated to inhibit arachidonic acid release thereby reducing the amount of substrate available for eicosanoid synthesis. To date, no studies have been reported on efficacy of salts of L651582 or its related compounds.
2.3 METABOLIC EFFECT OF OROTIC ACID
Any kind of organic or inorganic acid which is clinically compatible with the body may be selected to be reacted with AICA or 5-amino or substituted amino 1,2,3-triazoles. Especially desirable are orotic, lactic, succinic, maleic, citric, tartaric, gluconic, galactonic, hydrochloric, phosphoric and penta or poly hydroxycarboxylic acids.
Orotic acid is an intermediate in the pyrimidine pathway and its main source in the human and animal diet is bovine milk and its products. Orotic acid inhibited stimulation of protein synthesis and reduced the activity of ornithine decarboxylase, an enzyme which is believed to be a valuable index of cell proliferation. Grezelkowska K., et al., 1993, Endocrine Regulations 27:133-138. However, an orotate salt of AICA and/or 5-amino or substituted amino 1,2,3-triazoles has not been described for the prevention and treatment of neoplastic or other diseases.
2.4 CANCER GROWTH AND CHEMOTHERAPY
Cancer is a disease of inappropriate tissue accumulation. This derangement is most evident clinically when tumor tissue bulk compromises the function of vital organs. Contrary to what is generally thought, human malignant disorders are usually not diseases of rapid cell proliferation. In fact, the cells of most common cancers proliferate more slowly than many cells in normal tissues. It is a relatively slow accumulation of tumor tissue within vital organs that proves fatal to most patients who die of cancer.
Chemotherapeutic agents share one characteristic: they are usually more effective in killing or damaging malignant cells than normal cells. However, the fact that they do harm normal cells indicates their potential for toxicity. Understanding the use of chemotherapy requires a comprehension of both the drugs' mechanisms of action and the pathophysiology of cancer, which is rooted in deranged cellular and tissue growth.
Nearly all chemotherapeutic agents currently in use interfere with DNA synthesis, with the provision of precursors for DNA and RNA synthesis, or with mitosis. Such drugs are most effective against cycling cells. The mechanism of cell death after treatment with any single agent or combination of agents is complex and is likely to include more than one process. Because most clinically detectable tumors are composed mostly of noncycling cells, it is not surprising that chemotherapy is not always effective in eradicating cancer.
The strategy of cancer treatment is to shift tumor cells from a noncycling compartment to a cycling compartment. Several methods that promote this shift form the basis for combined-modality treatment. Surgery is most commonly used to reduce tumor size and thus facilitate reentry of cancer cells into the cell cycle. After a primary tumor is completely removed, microscopic metastases may remain at distant sites. Because of their small size, the micrometastases are composed principally of cycling cells. Small numbers of cells that remain at the primary tumor site are also likely to reenter the cell cycle. Thus, the remaining cancer cells are often susceptible to chemotherapy. Radiation therapy or chemotherapy alone can also be used to reduce tumor bulk and thus recruit cells into the cycling cell compartment. For example, the strategy of adjuvant chemotherapy for breast is based on these concepts. Weiss, R. B., and DeVita, Jr., V. T., 1979, Ann. Intern. Med. 91:251; Bonadonna, G., and Valagussa, P., 1988, Semin. Surg. Oncol. 4:250.
2.4.1 COMBINED CHEMOTHERAPY
Animal tumor investigations and human clinical trials have shown that drug combinations produce higher rates of objective response and longer survival than single agents. Frei, III, E., 1972, Cancer Res. 32:2593-2607. Combination drug therapy is, therefore, the basis for most chemotherapy employed at present. Combination chemotherapy uses the different mechanisms of action and cytotoxic potentials of multiple drugs. Although all chemotherapeutic drugs are most effective on cells that are synthesizing DNA, many agents--particularly the alkylating agents--can kill cells that are not cycling. Such agents are termed non-cell proliferation-dependent drugs. Some agents, including many of the antimetabolites and antibiotics, are most active against cells during DNA synthesis and are, therefore, termed cell-proliferation-dependent drugs. Repetitive administration of non-cell-proliferation-dependent agents can shrink tumor mass by killing cells in both the cycling and noncycling compartments of the tumor; the surviving cells will then move into the cycling compartment, where they are more susceptible to cell proliferation-dependent drugs. The combined use of agents less dependent on the cell cycle followed by those dependent on cell proliferation enhances tumor cell death. Each cycle of treatment kills a fixed fraction of cells, so repetitive cycles are required for cure. For example, a drug combination that kills 99.9 percent of cancer cells per treatment cycle would have to be repeated at least six times to eliminate an average tumor burden, if tumor cells did not regrow between cycles.
Several principles guide the selection of drugs to be used in combination. Drugs that are active individually are combined and administered in the highest doses the patient can tolerate and given as frequently as toxicity allows; drug combinations with limited overlaps of major toxicities are therefore preferable. The drugs selected should also have different mechanisms of action. This approach enhances cancer cell kill, reduces the chance that drug resistant cell populations will emerge, and disrupts cancer cell function by attacking multiple metabolic pathways. DeVita, V. T., et al., 1975, Cancer 35:98. However, even though the chemotherapeutic agents are more effective in killing or damaging malignant cells than normal cells, the fact that they do harm normal cells indicates their great potential for toxicity. For chemotherapy to be effective, the patient must be in good physiologic condition.
2.4.2 STRATEGIES IN THE USE OF CHEMOTHERAPY
Cancer treatment requires inhibition of a variety of factors including tumor cell proliferation, metastatic dissemination of cancer cells to other parts of the body, invasion, tumor-induced neovascularization, and enhancement of host immunological responses and cytotoxity. Conventional cancer chemotherapeutic agents have often been selected on the basis of their cytotoxicity to tumor cells. However, some anticancer agents have adverse effects on the patient's immunological system. Unfortunately, for the vast majority of conventional antineoplastic agents the margin between an effective dose and a toxic dose, i.e., the therapeutic index, is extremely low. Thus, it would be greatly advantageous if a cancer therapy or treatment could be developed that would afford noncytotoxic protection against factors that might lead to growth, progression and metastasis of invasive cancers.
2.5 DISEASES CHARACTERIZED BY ABNORMAL CELL PROLIFERATION
A number of clinical disease conditions are characterized by abnormal cell proliferation, e.g., psoriasis, eczema and endometriosis which result from localized spread of diseased cells. Other diseases associated with abnormal cell proliferation include, but are not limited to, systemic lupus erythematosus, arthritis, nerve conduction diseases and cystic fibrosis.